Modern Waterproofing Systems: Advancements in Osmotic Renders

The concrete gets wet or water gets below the membrane to create the osmotic cell by initial saturation, condensation, and liquid water within holes and voids below the membrane and vapor diffusion. Osmosis is the chemical-physical phenomenon whereby two liquid solutions spread into one another through a semipermeable membrane and is caused by the difference in concentration between the two liquids. Specially formulated cement systems, which are defined as ‘osmotic renders’, provided important waterproofing performances both in the occasional and permanent presence of rainwater, natural water, groundwater, etc.

Basic Working Principle

The particular adhesion of osmotic waterproofing systems, determined by the deep osmotic diffusion, also made them suitable for operating both in conditions of positive and negative water pressure. In building materials (and not only) adhesion and adherence are the result of two different mechanisms that can be present both separately and as more often happens, in coaction: mechanical adhesion and chemical adhesion. The osmotic or diffusive adhesion also comes into play in the osmotic process.

Mechanical Adhesion

Mechanical adhesion depends, to a large extent, on the degree of preparation of the substrates, in particular on their degree of cleaning and roughening as well as on their saturation.

Chemical Adhesion

Chemical adhesion, pertaining to molecular interactions, depends on the nature of the adhesive, its compatibility with the support, and, in turn, the degree of preparation of the surfaces.

Osmotic Or Diffusive Adhesion

In osmotic systems, there is also a specific adhesion, which is realized through the two coagent processes, of diffusion and reactive chemical gel deposition, often defined as osmotic or diffusive, dependent on the ‘osmotic capacity’ of the material and, once again, from the level of preparation of the surfaces.

Mapei‘s Osmotic Render: Planiseal 88

Mapei has a one-component osmotic cementitious system, Planiseal 88 where osmotic, diffusive, and mechanical adhesion is prevalent. Some of the important features and highlights for the application of the Planiseal 88 Waterproofing system are as below:

Surface Preparation

Among the essential conditions that must exist at the time of installation, it is necessary to consider the condition ‘saturated with a dry surface’, which can be defined as the ‘condition’ of support which, having wet a few hours before, has completely absorbed the water that was applied to it until it dried on the surface. In this way the support does not remove water from the material applied and the surface does not have veils of water that can interpose between the two materials, jeopardizing adhesion.

Proper Mixing

The wheelbarrow cannot be used in any way to ‘mix’ cementitious compounds and osmotic products in particular. The correct mixing must in fact take place either in special “mixers” and must be continued until a lump-free mixture is obtained, of the desired consistency. When mixed with water, Planiseal 88 becomes a fluid mortar that can be applied by trowel, brush, or spray with excellent adhesion to the substrate for complete waterproofing, even in the presence of negative pressure.

Preparation Of Mix

Preparing the mortar Pour 5-6 litres of water into a suitable container and slowly add the Planiseal 88 while blending with a mechanical mixer. Mix thoroughly for some minutes taking care to blend in all the unmixed powder deposited on the sides and bottom of the bucket, until the mortar is completely blended (free from lumps). Leave the mortar to stand for approximately Correct Distribution Of Stress In order to obtain a correct distribution of the stress, in correspondence with the connections between horizontal and vertical structures, it is essential to make a preliminary construction of connection joints suitable for the shape and dimensions to the geometry of the structures. Mapei offers Mapeband tapes and non-shrinkable grouts as per the site conditions.

Application Methodology Of Planiseal 88

Apply Planiseal 88 with a brush, trowel, or spray. Application by brush requires 2-3 coats. Make sure the previous coat is sufficiently dry before applying the next (generally 5-6 hours depending on the temperature and the absorption of the substrate. In order to have perfect adhesion between the coats, it is recommended not to exceed 24 hours). Consumption: approx. 1.5 kg/m2 per mm of thickness.

Highlights Of Planiseal 88

Planiseal 88 corresponds to the principles defined in EN 1504-9 (“Products and systems for protecting and repairing concrete structures: definitions, requirements, quality control and conformity assessment. General principles for the use of products and systems”) and the requirements of EN 1504-2 coating © according to the MC and IR principles (“Protection systems for concrete surfaces”) Comes in White & Grey Color (Can be used for positive and negative both sides of basement waterproofing to handle low to moderate hydrostatic pressure.)

Final Performance

With 22% mixing water - thickness 2.5 mm: It is tested in accordance to EN 1504-2 (surface protection system for concrete, where this membrane comes in the category of Moisture Control and Increase Resistivity coating.) Coefficient of permeability to free water (kg/m2·h0.5): Note w < 0.05 Class III (low permeability) according to EN 1062-1. Permeability to water vapor - equivalent air thickness SD - (m): SD < 1 Class I (permeable to water vapor). Bond strength on concrete (substrate in MC 0.40 - water/cement ratio = 0.40) according to EN 1766 (MPa): > 2

Advantages of Osmotic Renders On Crystalline Coatings

• Osmotic renders are compatible with potable water tanks whereas crystalline coatings are not.

• Osmotic renders are recommended for both concrete & masonry structures, crystalline coating only reacts with the free lime present in the concrete surface to give the reactive solution

• Osmotic renders bonding with concrete surface is more than 2M Pa gives extra assurance towards the integrity of the water tightness, whereas crystalline deeply penetrates in the pores and does not have any surface reaction.

• Osmotic renders can bear negative pressure to up to 1 ATM whereas crystalline coatings have no testing for negative pressure.

Conclusion

To protect the concrete surface, the Selection of waterproofing Treatments is very much crucial. For protection against moisture ingress, Planiseal 88 an osmotic render works for waterproofing and is useful for repairing underground masonries subject to water and moisture seepage in situations with negative pressure up to 1 atmosphere. Waterproofing basins, reservoirs, concrete or masonry tanks containing drinking water, waterproofing chemicals, or masonry tanks containing sewage water. Useful for both positive and negative side waterproofing. It can be applied to concrete or brick structures. Moreover, is classified as a protective protection coating for concrete as per EN 1504-2 guidelines.